1. Field of the Invention
The invention relates to a tobacco sheet of elevated filling power comprising tobacco particles, binder and moisturizer, as well as a method for producing such a sheet and an apparatus for producing such a sheet.
2. Description of the Prior Art
In the production of tobacco sheet or foil pieces from tobacco dust, tobacco fines and the tobacco stamps, it is known to extrude a foam product from said starting materials. A disadvantage here is the relatively high amount required of binders, in particular starch, which can easily lead to impairment of flavour, aroma and burning behaviour of smokable articles.
U.S. Pat. No. 3,098,492 and DE-OS 2,804,772 describe the extrusion of a foil or sheet by means of a slot nozzle; such a method would however be complicated and expensive if it were desired to produce therewith a sheet or foil having a filling power, comparable to tobacco and moreover a high tobacco content and low binder contents. This would be possible only with nozzle gap widths&lt;0.15 mm.
A factor here is that the filling power of the tobacco sheet depends decisively on the minimum possible thickness corresponding to a small nozzle gap width of the extrusion nozzle and for this reason the entire tobacco starting material must be present ground reliably to a miximum grain size. Tobacco particles in the raw mass of the tobacco starting material which are too large can easily clog such an extrusion nozzle, entailing complicated monitoring steps or requiring extremely reliable and thus complicated comminution methods.
The production of a sheet or foil by extrusion of the starting material using a slot nozzle in a roller nip is also known from U.S. Pat. No. 3,098,492, DE-OS 2,804,772 and GB-PS 1,459,218. In these cases as well, the aforementioned disadvantages of the low filling power compared with leaf material occur. In addition, the rollers forming the gap when operating with a slot nozzle can run with only a small peripheral speed and consequently a high torque is necessary, leading to high strain of the roller structure for relatively low throughput. An increase in the throughput can only be achieved by increasing the roller width; this in turn requires an extremely large slot nozzle, a stable roller structure and a large roller thickness in order to minimize the sagging of the rollers. Moreover, as a rule a multiple calender must be used because a single deformation step does not suffice for achieving the uniform required thickness.
In another known method (DE-OS 3,104,098, DE-PS 2,055,672, DE-PS 2,421,652, DE-PS 3,224,416 and GB-PS 1,459,218), of making tobacco foils or sheets by means of rollers or rolls, an extremely high amount of water must be added to the starting material, in the range of 30 to 50%, making subsequent drying necessary. This increases the necessary technical expenditure for the method. Moreover, in this case frequently undesired organic solvents are used, for example methylene chloride. Finally, in this case as well as a rule a multistage rolling apparatus or a calender is required.
A method and apparatus for reprocessing tobacco is known from DE-PS 3,339,247. Dust-like tobacco particles are worked with binders and possibly additives to give a plastifiable mixture which is extruded to form individual rodlike intermediate products. Said rodlike intermediate products are then processed to sheet pieces by reforming a cylindrical skein from the plasticized mixture in an extruder to a thin-walled continuously widening hollow body and split into threadlike intermediate products which become crimped. The threadlike crimped intermediate products are then cut to give the individual crimped fibre pieces. The intermediate products have a relatively dense structure which moreover due to the additives differs from the quality features of natural tobacco.
DE-OS 3,804,461 discloses a tobacco reconstitution method in which a mixture of tobacco particles, starch and binders is extruded with addition of water to form a striplike extrudate, the extrusion conditions and the recipe being such that the extrudate on leaving the exit aperture of the extruder nozzle assumes a cross-section which is greater than that of the exit aperture of the extruder nozzle, and the extrudate is stretched in its plastic phase to reduce its thickness dimensions, the stretching ratio being at least 1.5; the stretched extrudate is cut to give particles which each have a cellular structure and an integral skin. The stretching or drawing operation here is relatively complicated. If tearing of the tobacco sheet occurs in this case it leads to a loss of time and material during the production. Another disadvantage is the necessary high amount of binder, leading to impairment of the flavour and aroma.
DE-OS 3,804,459 discloses a tobacco reconstitution method in which a mixture of tobacco particles, starch and binder as well as water is supplied to an extruder, the operating conditions and the recipe being such that the water escapes from the striplike extrudate by evaporation in order to thereby expand the extrudate. After the cooling the extrudate is cut into particle size. The particles, each of which has a cellular inner structure and a skin on two oppositely disposed sides may be used as or in cigarette filling material. However, a disadvantage with this tobacco reconstitution method, as already indicated, is that large amounts of starch and binders are necessary and this leads to changes in the flavour and aroma of the tobacco material.
DE 33 28 663 C2 discloses a filling material of reconstituted tobacco material and a method for the production thereof. In this case, two separate sheet sections are locally adhered together, cavities forming between the two adhered sheet sections. This procedure is complicated, troublesome and provides sheet material of only low filling capacity. Moreover, the apparatus for carrying out the known method is complicated and involved.
DE 31 47 846 C2 relates to a method or a tobacco material with which by increasing the cell structure of the tobacco through a pressure reduction and pronounced temperature increase an expansion is achieved. However, such a method is possible only with natural tobacco material and is not suitable for reconstituted tobacco material because in this case no expandable cell structures are available.
EP 0 198 718 A2 discloses a method with which a reconstituted tobacco material of tobacco waste is expanded during the extrusion. The expansion is effected by a high extrusion temperature and an abrupt pressure reduction on leaving the extruder in conjunction with an adequate sheet thickness and a content of binder of at least about 10%. This production method is obviously based on completely different principles and also gives a completely different product which due to its high binder content is very unsatisfactory as regards its flavour, burning properties and the like.
EP 0 046 018 A1 also discloses a method for producing reconstituted tobacco material. However, this method is based only on the stiffening of the material and fixation of the stiffening. The reconstituted tobacco material is greatly overdried and thereafter again moisturized. As a result, the reconstituted tobacco material loses a greater part of its flavouring substances and becomes extremely critical in its handling because with increasing drying it becomes extremely brittle and friable. This method thus also results in a product which is unsatisfactory.
DE 38 19 534 C1 describes a thin compact tobacco product without air inclusions in which by extrusion a plurality of material rods or skeins are formed which are then rolled together again to form a monoply material layer.